Marine outboard engines have various systems that are necessary for their operation, or at least to facilitate and/or improve their operation. Such systems are for example, steering systems to steer the outboard engine, tilt and trim systems to adjust the vertical orientation of the outboard engine, throttle control systems to control the power generated by the engine, shifting systems to shift the direction of rotation of a propeller of the outboard engine, and variable pitch propeller systems to change the pitch of the propeller blades of the propeller.
Most of today's marine outboard engines have two or more of the above systems. Actuation of these systems can be done in different ways such as electrically (with electric motors or solenoids), mechanically (with linkages or push-pull cables), or with the use of hydraulic actuators.
FIG. 1 shows a typical hydraulic system 100′ using a hydraulic actuator 106′. The hydraulic system 100′ comprises a single pump 102′ electrically connected to an Electronic Control Unit (ECU) 104′ by connection 135′. The single pump 102′ supplies hydraulic fluid to the actuator 106′ for performing two actions. In the case of a steering system, the two actions performed by the actuator 106′ are steering right and left. In the case of a tilt/trim system, the two actions performed by the actuator 106′ are tilting up and down. A reservoir 105′ supplies the pump 102′ with hydraulic fluid. The pump 102′ connects to the actuator 106′ by a first fluid line 110a′ and by a second fluid line 110b′. The actuator 106′ is a piston-cylinder assembly comprising a first side 112a′ and a second side 112b′ (one side 112a′ or 112b′ for each action). Common types of actuators 106′ include linear displacement hydraulic actuators, or rotary hydraulic actuators. When the first fluid line 110a′ supplies the first side 112a′ of the actuator 106′ with hydraulic fluid, hydraulic pressure forces the first side 112a′ to expand which causes a steering motion in a first direction (e.g. port turn). When the second fluid line 110b′ supplies the second side 112b′ with hydraulic fluid, hydraulic pressure forces the second side 112b′ to expand which causes a steering motion in a second direction (e.g. starboard turn). Valves 115a′, 115b′ are positioned on fluid lines 110a′, 110b′ respectively. The valves 115a′, 115b′ are two-ways valves. They control which side of the piston-cylinder assembly is fed by the pump 102′, and also control the return of hydraulic fluid from the actuator 106′. The valves 115a′, 115b′ are electrically connected to the ECU 104′ which operates them by connection 137a′ and 137b′. The valves 115a′ and 115b′ are fluidly connected to the reservoir 106′ for the return of fluid by connections 139a′ and 139b′. 
Hydraulic systems, such as the hydraulic system 100′, rely on a single pump. When the pump fails, the actuator can no longer operate. In addition, the pump is limited in size for engine packaging reasons. Also, some manoeuvres require high volume flow rate that often exceed what the single pump can provide. Finally, when the single pump is designed for delivering high volume flow rates, packaging becomes cumbersome.
Therefore, there is a need for a hydraulic system that can provide pressurized fluid to the hydraulic actuator even if a pump fails or is deficient.
There is also a need for a hydraulic system that is able to provide sufficient hydraulic fluid when the level of hydraulic fluid required to perform an action is high.
Finally, there is a need for a hydraulic system that can be easily packaged within the constraints associated with outboard engines.